I have four CellPro 10S chargers, and when they are working I like them a lot. However, here are some things that have messed me up so far this year:

I started getting an "Unstable Voltage Error" on two of my chargers when I knew for absolute certain that my power supplies (I have two ...) were fine. It turned out that one charger had a loose fuse socket, and after I bent the tabs in the fuse holder, the error message went away. On the other charger it turned out that I had a stripped hole in the corner of the face plate where there is a capacitor jumper from one of the fuse holder terminals to the case, and I wasn't getting any compression of the eyelet at the end of the jumper. I used a bigger screw, and sanded off the black anodize from the face plate, and the main case to get better contact and the error mesage went away on the second charger.

I've shorted out the fuse between the middle terminals about a half dozen times now. What I do now is just solder a small 15 amp automotive fuse across the terminals, and the charger is fine until I short it out again.

I started getting a "Bad Cell Count Error" on two of my charger, when I knew that the cell count was just fine. It turned out that when I shorted out the middle termials one time, I also caused sparking in the balance connector on one of my batteries, and it half melted one of the balance connector terminals. I replaces it, and the error message went away on one of my chargers. On the other charger it turned out that one of the balance connector pins on the charger wasn't making good contact, so I bent it slightly at a small angle, and the error message went away on my second charger.

Right now I have four working chargers, except that one of them consistently reads about 400 mah lower than all of the others. I know it's the charger because if I swap batteries the problem stays with the charger, not the batteries. This problem's got me stumped, so right now I'm just living with it.